RF capabilities in the Tektronix MDO3104 oscilloscope are discussed and illustrated, using the RF noise floor as a signal source.
Hi and welcome to our 55th Test and Measurement video. The topic is Displaying and Exploring the RF menu in the amazing Tektronix MDO3104 oscilloscope.
First, we must make a distinction between the Fast Fourier Transform, or FFT as it is known, and the RF facility in this instrument. In the Tektronix 3000 Series oscilloscopes, FFT is a subdivision of Math. To see how this works, first press AFG to get a signal, which is the default sine wave. Then press Math. This brings up the Math menu, and the second choice is FFT. Here we see the frequency domain representation along with the time domain representation of the sine wave as accessed from the internal arbitrary function generator.
In the red frequency domain trace, notice the large spike at the left of the display. This is the fundamental. In a pure sine wave, there are no harmonics, so what we are seeing other than the fundamental is the oscilloscope’s noise floor. That was all by way of contrast to the main focus for today’s video, which is the RF menu in this Tektronix instrument. First press Default Setup so that there is nothing to confuse the issue. Then press RF to the right of the front panel under the number pad. You will see that Analog Channel One is thereby deactivated. In fact, RF cannot coexist with any of the analog channels. Pressing RF brings up the RF menu across the bottom of the display. When we press Spectrum Traces, a submenu appears to the right of the display. Spectrum Traces can be toggled On and Off. Be sure to leave them on for what follows.
The remaining four spectrum trace menu items are very interesting. They consist of three measurements that are shown in white or light brown, plus a reset button. They can be toggled on individually, in any combination or all at once. They depict cumulative measurements that at first change very quickly and then change progressively slower as higher levels are attained. The first of these is Average. Looking at the trace in juxtaposition with the noise floor, you can see how this works. Maximum Hold slowly rises as new heights are attained at each frequency. The Reset Spectrum Traces, as its name implies, does just that, and then the light brown trace once again starts to rise. The Minimum Hold works in the same way, showing the lowest amplitude value at each frequency. Similarly, it can be reset. Here we see all three of these turned on and working simultaneously. They can be reset, to begin anew.
Returning to the RF Menu, the next item is Spectrogram, which was covered extensively in a previous video. Pressing spectrogram, the relevant submenu appears to the right of the display, and Spectrogram can be turned On. The graphic slowly rises from the bottom to the top of the display. One might think that is because it is loading, but in reality this corresponds to the passage of time, which is represented on the Y-axis. The X-axis is defined in terms of frequency. Amplitude is shown by color, warm colors representing higher amplitude and cool colors representing lower amplitude. The speckled appearance of the Spectrogram at present is due to the noise floor in the trace, as shown in the frequency domain view in the lower portion of the screen. If you turn off Spectrogram and press More, on-screen instructions for performing RF Signal Path Compensation appear, and this should be done before any critical RF measurements are undertaken.
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